U.S. patent number 10,035,536 [Application Number 15/415,595] was granted by the patent office on 2018-07-31 for ball screw and steering system.
This patent grant is currently assigned to JTEKT CORPORATION. The grantee listed for this patent is JTEKT CORPORATION. Invention is credited to Masayuki Tsukagoshi, Eiji Yamazaki.
United States Patent |
10,035,536 |
Yamazaki , et al. |
July 31, 2018 |
Ball screw and steering system
Abstract
A ball screw in a steering system has a groove between the inner
peripheral surface of a cylindrical ball nut through which a
steered shaft extends and the outer peripheral surface of the
steered shaft, and balls are accommodated in the groove. The balls
rolling and flowing in the groove are returned from downstream to
upstream via deflectors and a return passage member disposed in the
ball nut. The return passage member has a first connection portion
curved to connect one end of a linear portion of the return passage
member to the first deflector, and a second connection portion
curved to connect the other end of the linear portion to the second
deflector. Each connection portion has an opening that opens in the
return passage member longitudinal end face and an opening that
opens in the return passage member outer periphery of toward the
centerline of the ball nut.
Inventors: |
Yamazaki; Eiji (Nagoya,
JP), Tsukagoshi; Masayuki (Okazaki, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JTEKT CORPORATION |
Osaka-shi, Osaka |
N/A |
JP |
|
|
Assignee: |
JTEKT CORPORATION (Osaka,
JP)
|
Family
ID: |
57956147 |
Appl.
No.: |
15/415,595 |
Filed: |
January 25, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170225706 A1 |
Aug 10, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Feb 4, 2016 [JP] |
|
|
2016-019847 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16H
25/2223 (20130101); B62D 5/0448 (20130101); F16H
25/2214 (20130101); B62D 3/06 (20130101); F16H
2025/2081 (20130101); F16H 2025/2096 (20130101) |
Current International
Class: |
B62D
5/04 (20060101); F16H 25/22 (20060101); F16H
25/20 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2 218 942 |
|
Aug 2010 |
|
EP |
|
2 784 351 |
|
Oct 2014 |
|
EP |
|
2004-353835 |
|
Dec 2004 |
|
JP |
|
2008-039050 |
|
Feb 2008 |
|
JP |
|
Other References
Jun. 13, 2017 Extended Search Report issued in European Patent
Application No. 17154036.2. cited by applicant.
|
Primary Examiner: Hurley; Kevin
Attorney, Agent or Firm: Oliff PLC
Claims
What is claimed is:
1. A ball screw comprising: a ball nut; a ball screw shaft
extending through the ball nut; a first deflector; a second
deflector; a return passage member including: (i) a linear portion
located between the first deflector and the second deflector in the
ball nut, (ii) a first connection portion curved to serve as a
portion connecting one end of the linear portion to the first
deflector, and (iii) a second connection portion curved to serve as
a portion connecting another end of the linear portion to the
second deflector, each of the first connection portion and the
second connection portion having an opening in an outer periphery
and an end face of the return passage member, each of the openings
in the outer periphery opens toward a centerline of the ball nut
and is closed by an outer surface of the ball nut; and a groove
formed between an outer peripheral surface of the ball screw shaft
and an inner peripheral surface of the ball nut, the groove
accommodating a plurality of balls, wherein: the ball screw
converts rotary motion and linear motion and vice versa between the
ball nut and the ball screw shaft via the plurality of balls and
the groove, and when performing the conversion: the ball screw
deflects the plurality of balls rolling in the groove by the first
deflector, then transfers the plurality of balls to the second
deflector through the return passage member, and returns the
plurality of balls from the second deflector to the groove, or the
ball screw deflects the plurality of balls rolling in the groove by
the second deflector, then transfers the plurality of balls to the
first deflector through the return passage member, and returns the
plurality of balls from the first deflector to the groove; the
first deflector and the second deflector are disposed in the ball
nut so as to extend along the groove; each of the first connection
portion and the second connection portion is curved so that a
centerline of each of the first connection portion and the second
connection portion forms a curve; a center of the curve of the
centerline of the first connection portion is located in a region
that is located closer to a position where the first deflector
deflects the plurality of balls than an axis of the linear portion
of the return passage member in a direction perpendicular to the
axis of the linear portion, and the center of the curve of the
centerline of the first connection portion is located closer to a
middle in an axial direction of the linear portion than the first
deflector in the axial direction of the linear portion; and a
center of the curve of the centerline of the second connection
portion is located in a region that is located closer to a position
where the second deflector returns the plurality of balls than the
axis of the linear portion of the return passage member in the
direction perpendicular to the axis of the linear portion, and the
center of the curve of the centerline of the second connection
portion is located closer to the middle in the axial direction of
the linear portion than the second deflector in the axial direction
of the linear portion.
2. The ball screw according to claim 1, wherein: the opening in the
outer periphery of the first connection portion opens on a side of
the first connection portion which faces the centerline of the ball
nut along an entire longitudinal length of the first connection
portion, the opening in the outer periphery of the second
connection portion opens on a side of the second connection portion
which faces the centerline of the ball nut along an entire
longitudinal length of the second connection portion, the linear
portion has an opening in an outer periphery of the linear portion,
and the opening of the linear portion opens on a side of the linear
portion which faces the centerline of the ball nut along an entire
longitudinal length of the linear portion, the opening connects to
the opening in the outer periphery of the first connection portion
and the opening in the outer periphery of the second connection
portion, and the opening is closed by the outer surface of the ball
nut.
3. The ball screw according to claim 2, wherein: each of the first
connection portion, the linear portion, and the second connection
portion has a pair of standing walls extending parallel to each
other in a direction in which the plurality of balls flow in the
return passage member, and an inter-wall portion connecting ends of
the pair of standing walls which are located farther away from the
centerline of the ball nut, and the opening in the outer periphery
of the first connection portion, the opening in the outer periphery
of the linear portion, and the opening in the outer periphery of
the second connection portion are formed between other ends of the
pair of standing walls which are located closer to the centerline
of the ball nut.
4. The ball screw according to claim 1, wherein the return passage
member is fitted in a groove formed in an outer peripheral surface
of the ball nut, and a bottom surface of the groove serves as the
outer surface of the ball nut which closes the opening in the outer
periphery.
5. The ball screw according to claim 1, wherein: a first passage
hole for the plurality of balls, which is formed inside the first
deflector, is curved at an end located on a return passage member
side, a centerline of the passage hole curved at the end is
continuous with the centerline of the first connection portion at a
connection point with the centerline of the first connection
portion, and the centerline of the passage hole curved at the end
and the centerline of the first connection portion have a common
tangent at the connection point, and a second passage hole for the
plurality of balls, which is formed inside the second deflector, is
curved at an end located on the return passage member side, a
centerline of the passage hole curved at the end is continuous with
the centerline of the second connection portion at a connection
point with the centerline of the second connection portion, and the
centerline of the passage hole curved at the end and the centerline
of the second connection portion have a common tangent at the
connection point.
6. A steering system comprising: the ball screw according to claim
1; and a steered shaft, wherein the ball screw shaft forms a part
of the steered shaft.
7. The steering system according to claim 6, further comprising: a
motor; and a cylindrical member that transmits torque of the motor
to the ball nut, the cylindrical member being fitted on the outer
peripheral surface of the ball nut, and an inner peripheral surface
of the cylindrical member contacting the return passage member.
Description
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2016-019847 filed
on Feb. 4, 2016 including the specification, drawings and abstract,
is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ball screws and steering
systems.
2. Description of the Related Art
Japanese Patent Application Publication No. 2004-353835 (JP
2004-353835 A) describes that a ball screw includes a ball nut and
a ball screw shaft and functions to convert rotary motion of the
ball nut to linear motion of the ball screw shaft. In such a ball
screw, a plurality of balls are accommodated in grooves between the
outer peripheral surface of the ball screw shaft and the inner
peripheral surface of the ball nut, so that the ball screw converts
rotary motion to linear motion and vice versa between the ball nut
and the ball screw shaft via the plurality of balls and the
grooves. For example, the above ball screw is used in a vehicle
steering system to convert rotary motion of the ball nut, which is
made by an assist actuator, to axial linear motion of a steered
shaft (rack shaft).
In addition to ball screws, roller screws such as the one described
in Japanese Patent Application Publication No. 2008-39050 (JP
2008-39050 A) are also known in the art. The roller screws use
cylindrical rollers as rolling elements instead of the balls. In
both the ball screws and the roller screws, the plurality of
rolling elements roll in the grooves and thus move together in the
grooves when the nut rotates relative to the shaft. It is therefore
necessary to return the rolling elements in the grooves from
downstream to upstream in the direction in which the rolling
elements move so as to recirculate the rolling elements. Structures
having a first deflector (recirculating element), a second
deflector (recirculating element), and a return pipe, such as the
one described in JP 2008-39050 A, are known as an example of
structures that return the rolling elements in the grooves from
downstream to upstream. The first deflector deflects the rolling
elements rolling in the grooves, the return pipe carries the
rolling elements from the first deflector to the second deflector,
and the second deflector returns the deflected rolling elements to
the grooves.
Specifically, the nut is provided with the first and second
deflectors extending along the grooves, and the first and second
deflectors are connected by the return pipe extending linearly in
the axial direction of the nut. In this case, the rolling elements
are deflected from the grooves by the first deflector in a
downstream part of the grooves. The deflected rolling elements are
then carried to the second deflector through the return pipe and
are returned from the second deflector to the grooves.
However, if the direction in which the rolling elements flow
changes at an acute angle in the connection portion between the
first deflector and the return pipe and the connection portion
between the return pipe and the second deflector, the rolling
elements may not be able to smoothly pass through these connection
portions.
The return pipe may be curved in portions connected to the first
and second deflectors so that the direction in which the rolling
elements flow changes gradually in these portions. However, if
these portions of the return pipe are curved, these portions may be
deformed, and the inside diameters of these portions, specifically
the inside diameters of the return pipe in the direction of the
radius of curvature of the curves of these portions, may be
reduced. The rolling elements are therefore subjected to increased
resistance when passing through these portions, and such increased
resistance hinders smooth flow of the rolling elements.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a ball screw
in which balls serving as rolling elements can flow smoothly and a
steering system.
According to one aspect of the present invention, a ball screw
includes: a ball nut; a ball screw shaft extending through the ball
nut; a first deflector; a second deflector; and a return passage
member. The ball screw has a groove formed between an outer
peripheral surface of the ball screw shaft and an inner peripheral
surface of the ball nut and accommodating a plurality of balls, and
converts rotary motion and linear motion and vice versa between the
ball nut and the ball screw shaft via the plurality of balls and
the groove. When carrying out the conversion, the ball screw
deflects the balls rolling in the groove by the first deflector,
then carries the balls to the second deflector through the return
passage member, and returns the balls from the second deflector to
the groove, or the ball screw deflects the balls rolling in the
groove by the second deflector, then carries the balls to the first
deflector through the return passage member, and returns the balls
from the first deflector to the groove. The first deflector and the
second deflector are disposed in the ball nut so as to extend along
the groove. The return passage member has a linear portion located
between the first deflector and the second deflector in the ball
nut, a first connection portion curved to serve as a portion
connecting one end of the linear portion to the first deflector,
and a second connection portion curved to serve as a portion
connecting the other end of the linear portion to the second
deflector. Each of the first and second connection portions has an
opening in an outer periphery and an end face of the return passage
member, and the opening in the outer periphery opens toward a
centerline of the ball nut and is closed by an outer surface of the
ball nut.
In the above configuration, the process of curving both
longitudinal ends of the return passage member in order to form the
first and second connection portions can be performed with a male
die being inserted into the return passage member from the openings
in the outer periphery at both longitudinal ends of the return
passage member. This can restrain the dimension between the
opposing inner walls of each of the first and second connection
portions (hereinafter referred to as the "inside diameter" for
convenience), namely the inside diameters of the first and second
connection portions in a direction of the radius of curvature of
the curves of the first and second connection portions, from being
reduced by deformation of both longitudinal ends of the return
passage member when both longitudinal ends of the return passage
member are curved. If the inside diameters of the first and second
connection portions are reduced as described above, the balls in
the groove are subjected to increased resistance when they pass
through the first connection portion and the second connection
portion to recirculate through the first deflector, the return
passage member, and the second deflector in the ball screw having
the return passage member attached thereto. Such increased
resistance hinders smooth flow of the balls. However, since
reduction in inside diameter of the first and second connection
portions is restrained, an increase in resistance the balls are
subjected to when passing through the first and second connection
portions can be restrained, whereby smooth flow of the balls can be
achieved, and fluctuations in rotation resistance of the ball nut
can be reduced.
The first and second connection portions may be curved as follows.
Each of the first and second connection portions may be curved so
that its centerline forms a curve. A center of the curve of the
centerline of the first connection portion may be present in a
region that is located closer to a position where the first
deflector deflects the balls than an axis of the linear portion of
the return passage member is in a direction perpendicular to the
axis of the linear portion and that is located closer to a middle
in an axial direction of the linear portion than the first
deflector is in the axial direction of the linear portion, and a
center of the curve of the centerline of the second connection
portion may be present in a region that is located closer to a
position where the second deflector returns the balls than the axis
of the linear portion of the return passage member is in the
direction perpendicular to the axis of the linear portion and that
is located closer to the middle in the axial direction of the
linear portion than the second deflector is in the axial direction
of the linear portion.
The opening in the outer periphery of the first connection portion
may open on a side of the first connection portion which faces the
centerline of the ball nut along an entire longitudinal length of
the first connection portion, the opening in the outer periphery of
the second connection portion may open on a side of the second
connection portion which faces the centerline of the ball nut along
an entire longitudinal length of the second connection portion, and
the linear portion may have an opening in its outer periphery. In
this case, the opening of the linear portion may open on a side of
the linear portion which faces the centerline of the ball nut along
an entire longitudinal length of the linear portion, may connect to
the opening in the outer periphery of the first connection portion
and the opening in the outer periphery of the second connection
portion, and may be closed by the outer surface of the ball
nut.
In this configuration, the openings in the outer periphery of the
return passage member are formed along an entire longitudinal
length of the return passage member. Accordingly, the first and
second connection portions can be formed by curving both
longitudinal ends of the return passage member with the male die
being inserted into the return passage member along the entire
length of the return passage member from these openings. In this
case, when both longitudinal ends of the return passage member are
curved in order to form the first and second connection portions,
the male die has been inserted in the return passage member along
the entire longitudinal length of the return passage member. This
can restrain the influence of the process of curving both
longitudinal ends of the return passage member on the linear
portion of the return passage member.
Each of the first connection portion, the linear portion, and the
second connection portion may have a pair of standing walls
extending parallel to each other in a direction in which the balls
flow in the return passage member, and an inter-wall portion
connecting one ends of the standing walls which are located farther
away from the centerline of the ball nut. In this case, the opening
in the outer periphery of the first connection portion, the opening
in the outer periphery of the linear portion, and the opening in
the outer periphery of the second connection portion are formed
between the other ends of the pair of standing walls which are
located closer to the centerline of the ball nut.
The return passage member may be fitted in a groove formed in an
outer peripheral surface of the ball nut, and a bottom surface of
the groove may serve as the outer surface of the ball nut which
closes the opening in the outer periphery.
In this configuration, the return passage member is fitted in the
groove formed in the outer peripheral surface of the ball nut and
is connected to the first and second deflectors. The return passage
member connecting the first and second deflectors can therefore be
easily held in the ball nut.
In the ball screw of the above aspect, a passage hole for the
balls, which is formed inside the first deflector, may be curved at
its end located on the return passage member side, a centerline of
the passage hole curved at its end may be continuous with the
centerline of the first connection portion at a connection point
with the centerline of the first connection portion, and the
centerline of the passage hole curved at its end and the centerline
of the first connection portion may have a common tangent at the
connection point. A passage hole for the balls, which is formed
inside the second deflector, may be curved at its end located on
the return passage member side, a centerline of the passage hole
curved at its end may be continuous with the centerline of the
second connection portion at a connection point with the centerline
of the second connection portion, and the centerline of the passage
hole curved at its end and the centerline of the second connection
portion may have a common tangent at the connection point.
The ball screw may be applied to a steering system including a
steered shaft. In this case, a part of the steered shaft serves as
the ball screw shaft of the ball screw.
In the above configuration, a steering system that operates
smoothly can be implemented due to reduced fluctuations in rotation
resistance of the ball nut.
The steering system may further include: a motor; and a cylindrical
member that transmits torque of the motor to the ball nut. The
cylindrical member may be fitted on the outer peripheral surface of
the ball nut, and an inner peripheral surface of the cylindrical
member may contact the return passage member.
In the above configuration, the return passage member disposed in
the ball nut is held against the ball nut by the inner peripheral
surface of the cylindrical member fitted on the outer peripheral
surface of the ball nut. This can restrain the return passage
member from coming off from the ball nut due to clogging of the
return passage member with the balls or due to the centrifugal
force generated by rotation of the ball nut.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and further features and advantages of the invention
will become apparent from the following description of example
embodiments with reference to the accompanying drawings, wherein
like numerals are used to represent like elements and wherein:
FIG. 1 is a schematic view showing the overall configuration of a
steering system;
FIG. 2 is a sectional view showing the structure of a ball screw
provided in the steering system;
FIG. 3 is a plan view showing deflectors and a return passage
member of a ball recirculation system provided in a ball nut of the
ball screw;
FIG. 4 is a perspective view showing attachment recesses and an
attachment groove which are formed in the outer peripheral surface
of the ball nut;
FIG. 5 is a sectional view showing a connection portion of the
return passage member taken along line A-A and viewed in the
direction of arrows A in FIG. 3;
FIG. 6 is a sectional view showing a connection portion of the
return passage member taken along line B-B and viewed in the
direction of arrows B in FIG. 3;
FIG. 7 is a sectional view showing a linear portion of the return
passage member taken along line C-C and viewed in the direction of
arrows C in FIG. 3;
FIG. 8 is a schematic view showing how to produce the return
passage member;
FIG. 9 is a schematic view showing a projecting portion of a male
die of a press die that is used to produce the return passage
member;
FIG. 10 is a plan view showing the produced return passage member;
and
FIG. 11 is a schematic view of a material for forming the return
passage member (first and second connection portions) being
sandwiched between dies of a press machine.
DETAILED DESCRIPTION OF EMBODIMENTS
An embodiment of a ball screw and a steering system will be
described below with reference to FIGS. 1 to 11.
As shown in FIG. 1, a steering system of a vehicle includes a
steering wheel 1 that is operated by a driver, and a column shaft 2
connecting to the steering wheel 1. The column shaft 2 is connected
to an intermediate shaft 3 and a pinion shaft 4. The pinion shaft 4
is connected to a steered shaft 6 via a rack and pinion mechanism
5. The steered shaft 6 is supported by a housing 7 so that the
steered shaft 6 can move in the axial direction thereof and does
not rotate about its axis. The steered shaft 6 has its both axial
ends connected to knuckles 11 of steered wheels 10 of the vehicle
via ball joints 8 and tie rods 9.
When the driver of the vehicle turns the steering wheel 1, the
column shaft 2 rotates about its central axis according to the
turning of the steering wheel 1. When the column shaft 2 rotates in
this manner, the intermediate shaft 3 and the pinion shaft 4 rotate
about their central axes accordingly. The rack and pinion mechanism
5 converts the rotation of the pinion shaft 4 to axial linear
movement of the steered shaft 6. The steered angle of the steered
wheels 10 is changed by axial displacement of the steered shaft
6.
The steering system is provided with an assist device 12. The
assist device 12 assists in axial movement of the steered shaft 6
which is made when the steering wheel 1 is turned by the driver.
The assist device 12 includes a cylindrical ball nut 13, a motor
14, a ball screw 15, and a belt speed reduction mechanism 41. The
steered shaft 6 extends through the ball nut 13. The motor 14
functions as an actuator that rotates the ball nut 13. The ball
screw 15 converts rotary motion of the ball nut 13 to axial linear
motion of the steered shaft 6. The belt speed reduction mechanism
41 amplifies rotation torque of the motor 14 to transmit the
amplified rotation torque to the ball nut 13. Forward rotation of
the motor 14 (ball nut 13) assists in linear movement of the
steered shaft 6 to one side in the axial direction, and reverse
rotation of the motor 14 (ball nut 13) assists in linear movement
of the steered shaft 6 to the other side in the axial
direction.
The structure of the ball screw 15 will be described in detail
below.
As shown in FIG. 2, the ball screw 15 has grooves 17 between the
outer peripheral surface of the steered shaft 6 extending through
the ball nut 13 and the inner peripheral surface of the ball nut
13, and a multiplicity of balls 16 are accommodated in the grooves
17. The ball screw 15 converts rotary motion to linear motion and
vice versa between the ball nut 13 and the steered shaft 6 via the
multiplicity of balls 16 and the grooves 17. The ball screw 15 of
this example converts rotary motion of the ball nut 13 to linear
motion of the steered shaft 6. A driven pulley 71, which is driven
to rotate by the motor 14, is fitted on the outer peripheral
surface of the ball nut 13. The driven pulley 71 is a cylindrical
member that transmits torque of the motor 14 (FIG. 1) to the ball
nut 13. Instead of the driven pulley 71, a motor shaft, which is
driven to rotate by the motor 14, may be used as the cylindrical
member and fitted on the outer peripheral surface of the ball nut
13.
When the ball screw 15 converts rotary motion of the ball nut 13 to
linear motion of the steered shaft 6, the multiplicity of balls 16
roll in the grooves 17 and thus move together in the grooves 17. It
is therefore necessary to return the balls 16 in the grooves 17
from downstream to upstream in the grooves 17 so as to recirculate
the balls 16. For this purpose, the ball screw 15 is provided with
a ball recirculation system that implements the recirculation of
the balls 16. The ball recirculation system includes a first
deflector 18, a second deflector 19, and a return passage member
20. The first and second deflectors 18, 19 deflect the balls 16
from the grooves 17 and return the balls 16 to the grooves 17. The
return passage member 20 carries the balls 16 between the first and
second deflectors 18, 19.
When the ball nut 13 rotates in the forward direction, the first
deflector 18 serves to deflect the balls 16 from the grooves 17,
and the second deflector 19 serves to return the balls 16 to the
grooves 17. In this case, the balls 16 flowing in the grooves 17
are deflected by the first deflector 18 located downstream in the
flow of the balls 16. The balls 16 thus deflected are then carried
through the return passage member 20 to the second deflector 19
located upstream in the flow of the balls 16 in the grooves 17. The
balls 16 carried to the second deflector 19 are returned from the
second deflector 19 to the grooves 17.
When the ball nut 13 rotates in the reverse direction, the second
deflector 19 serves to deflect the balls 16 from the grooves 17,
and the first deflector 18 serves to return the balls 16 to the
grooves 17. In this case, the balls 16 flowing in the grooves 17
are deflected by the second deflector 19 located downstream in the
flow of the balls 16. The balls 16 thus deflected are then carried
through the return passage member 20 to the first deflector 18
located upstream in the flow of the balls 16 in the grooves 17. The
balls 16 carried to the first deflector 18 are returned from the
first deflector 18 to the grooves 17.
As shown in FIG. 3, the first deflector 18 and the second deflector
19 are provided in the ball nut 13 so as to extend along the
grooves 17 (FIG. 2). The return passage member 20 has a linear
portion 21, a first connection portion 22, and a second connection
portion 23. The linear portion 21 is formed between the first and
second deflectors 18, 19 in the ball nut 13. The first connection
portion 22 is curved so as to connect one end of the linear portion
21 to the first deflector 18. The second connection portion 23 is
curved so as to connect the other end of the linear portion 21 to
the second deflector 19.
Each of the first and second connection portions 22, 23 is curved
so that its centerline forms a curve. If a small part of the
centerline of each of the first and second connection portions 22,
23 is approximated by an arc to consider the radius of curvature,
the approximate arc has a center. The center of the approximate arc
is hereinafter referred to as the "center of the curve of the
centerline." The center C1 of the curve of the centerline of the
first connection portion 22 is present in a region that is located
closer to the position where the first deflector 18 deflects the
balls 16 than the axis L1 of the linear portion 21 is in the
direction perpendicular to the axis L1 of the linear portion 21
(the vertical direction in FIG. 3) and that is located closer to
the middle in the axial direction of the linear portion 21 than the
first deflector 18 is in the axial direction of the linear portion
21. The center C2 of the curve of the centerline of the second
connection portion 23 is present in a region that is located closer
to the position where the second deflector 19 returns the balls 16
to the grooves 17 than the axis L1 of the linear portion 21 is in
the direction perpendicular to the axis L1 of the linear portion 21
and that is located closer to the middle in the axial direction of
the linear portion 21 than the second deflector 19 is in the axial
direction of the linear portion 21.
The inside of the first connection portion 22 communicates with a
passage hole 18a formed in the first deflector 18. The passage hole
18a is curved at its end located on the return passage member 20
side, and the centerline of the passage hole 18a curved at its end
is continuous with the centerline of the first connection portion
22 at the connection point with the centerline of the first
connection portion 22. The centerline of the passage hole 18a
curved at its end and the centerline of the first connection
portion 22 have a common tangent at the connection point. Since the
passage hole 18a is curved as described above, the first deflector
18 changes the direction in which the balls 16 flow in the passage
hole 18a between the direction in which the grooves 17 extend and
the direction in which the first connection portion 22 is
curved.
The inside of the second connection portion 23 communicates with a
passage hole 19a formed in the second deflector 19. The passage
hole 19a is curved at its end located on the return passage member
20 side, and the centerline of the passage hole 19a curved at its
end is continuous with the centerline of the second connection
portion 23 at the connection point with the centerline of the
second connection portion 23. The centerline of the passage hole
19a curved at its end and the centerline of the second connection
portion 23 have a common tangent line at the connection point.
Since the passage hole 19a is curved as described above, the second
deflector 19 changes the direction in which the balls 16 flow in
the passage hole 19a between the direction in which the grooves 17
extend and the direction in which the second connection portion 23
is curved.
As shown in FIG. 4, the ball nut 13 has attachment recesses 24, 25
and an attachment groove 26 in its outer peripheral surface. The
attachment recesses 24, 25 are recesses to which the first
deflector 18 and the second deflector 19 are attached,
respectively, and are formed so as to extend along the grooves 17.
The attachment groove 26 is a groove to which the return passage
member 20 (FIG. 3) is attached, and is formed between the
attachment recesses 24, 25 so as to extend in the axial direction
of the ball nut 13.
The first and second deflectors 18, 19 are attached to the ball nut
13 by fitting the first deflector 18 in the attachment recess 24
and fitting the second deflector 19 in the attachment recess 25.
The return passage member 20 is attached to the ball nut 13 by
fitting the return passage member 20 in the attachment groove 26.
As shown in FIG. 3, the inside of the first connection portion 22
of the return passage member 20 communicates with the passage hole
18a of the first deflector 18 and the inside of the second
connection portion 23 of the return passage member 20 communicates
with the passage hole 19a of the second deflector 19 by attaching
the first deflector 18, the second deflector 19, and the return
passage member 20 to the ball nut 13 in this manner.
FIGS. 5 to 7 show the first connection portion 22 taken along line
A-A and viewed in the direction of arrows A in FIG. 3, the second
connection portion 23 taken along line B-B and viewed in the
direction of arrows B in FIG. 3, and the linear portion 21 taken
along line C-C and viewed in the direction of arrows C in FIG. 3,
respectively.
As shown in FIG. 5, the first connection portion 22 has openings
22a, 22b. The opening 22a opens in an end face of the return
passage member 20, and the opening 22b opens in the outer periphery
of the return passage member 20. The opening 22a in the end face of
the return passage member 20 communicates with the passage hole 18a
(FIG. 3) of the first deflector 18. The opening 22b in the outer
periphery of the return passage member 20 opens toward the
centerline of the ball nut 13 (downward in FIG. 5). This opening
22b opens on the side of the first connection portion 22 which
faces the centerline of the ball nut 13 (i.e., opens on the lower
side of the first connection portion 22 in FIG. 5) along the entire
longitudinal length of the first connection portion 22, and is
closed by the outer surface of the ball nut 13 (the bottom surface
of the attachment groove 26). The inner peripheral surface of the
driven pulley 71 fitted on the outer peripheral surface of the ball
nut 13 contacts the first connection portion 22 of the return
passage member 20.
As shown in FIG. 6, the second connection portion 23 has openings
23a, 23b. The opening 23a opens in an end face of the return
passage member 20, and the opening 23b opens in the outer periphery
of the return passage member 20. The opening 23a in the end face of
the return passage member 20 communicates with the passage hole 19a
(FIG. 3) of the second deflector 19. The opening 23b in the outer
periphery of the return passage member 20 opens toward the
centerline of the ball nut 13 (downward in FIG. 6). This opening
23b opens on the side of the second connection portion 23 which
faces the centerline of the ball nut 13 (i.e., opens on the lower
side of the second connection portion 23 in FIG. 6) along the
entire longitudinal length of the second connection portion 23, and
is closed by the outer surface of the ball nut 13 (the bottom
surface of the attachment groove 26). The inner peripheral surface
of the driven pulley 71 also contacts the second connection portion
23 of the return passage member 20.
As shown in FIG. 7, the linear portion 21 has an opening 21b. The
opening 21b opens on the side of the linear portion 21 which faces
the centerline of the ball nut 13 (i.e., opens on the lower side of
the linear portion 21 in FIG. 7) along the entire longitudinal
length of the linear portion 21. This opening 21b connects to the
opening 22b (FIG. 5) in the outer periphery of the first connection
portion 22 and the opening 23b (FIG. 6) in the outer periphery of
the second connection portion 23, and is closed by the outer
surface of the ball nut 13 (the bottom surface of the attachment
groove 26). The inner peripheral surface of the driven pulley 71
also contacts the linear portion 21 of the return passage member
20.
As can be seen from FIGS. 5 to 7, each of the first connection
portion 22, the second connection portion 23, and the linear
portion 21 has a pair of standing walls 27 extending parallel to
each other in the direction in which the balls 16 flow in the
return passage member 20 (the direction crossing the plane of paper
in FIGS. 5 to 7). Each of the first connection portion 22, the
second connection portion 23, and the linear portion 21 further has
an arc-shaped inter-wall portion 28 connecting one ends of the pair
of standing walls 27 which are located farther away from the
centerline of the ball nut 13 (the upper ends of the pair of
standing walls 27 in FIGS. 5 to 7). The opening 22b (FIG. 5) in the
outer periphery of the first connection portion 22, the opening 23b
(FIG. 6) in the outer periphery of the second connection portion
23, and the opening 21b (FIG. 7) in the outer periphery of the
linear portion 21 are formed to extend between the other ends of
the pair of standing walls 27 which are located closer to the
centerline of the ball nut 13 (the lower ends of the pair of
standing walls 27 in FIGS. 5 to 7).
As shown in FIG. 3, the pair of standing walls 27 of the first
connection portion 22 are curved, and the centers of the curves of
the pair of standing walls 27 are located at the center C1 shown in
FIG. 3. The outer standing wall 27 in the radial direction of the
curve of the first connection portion 22 has a larger radius
curvature than the inner standing wall 27 in the radial direction
of the curve of the first connection portion 22. The difference in
radius of curvature between these outer and inner standing walls 27
is slightly larger than the diameter of the balls 16.
The pair of standing walls 27 of the second connection portion 23
are also curved, and the centers of the curves of the pair of
standing walls 27 are located at the center C2 in FIG. 3. The outer
standing wall 27 in the radial direction of the curve of the second
connection portion 23 has a larger radius of curvature than the
inner standing wall 27 in the radial direction of the curve of the
second connection portion 23. The difference in radius of curvature
between these outer and inner standing walls 27 is slightly larger
than the diameter of the balls 16.
The return passage member 20 of the ball recirculation system
provided in the steering system has the first connection portion 22
that is curved so as to connect one end of the linear portion 21
provided between the first and second deflectors 18, 19 to the
first deflector 18. The return passage member 20 further has the
second connection portion 23 that is curved so as to connect the
other end of the linear portion 21 to the second deflector 19.
When the return passage member 20 is produced, the first and second
connection portions 22, 23 are curved as follows.
FIGS. 8 to 10 schematically show how to produce the return passage
member 20 and a machine that is used to produce the return passage
member 20. As shown in FIG. 8, the return passage member 20 is
produced by placing a plate-like material 29 of the return passage
member 20 between a female die 30 and a male die 31 of a press die
and then pressing the female die 30 against the male die 31.
The male die 31 has a projecting portion 32 projecting toward the
female die 30. FIG. 9 shows the projecting portion 32 as viewed
from above in FIG. 8. The outer shape of the projecting portion 32
corresponds to the inner shape of the return passage member 20
(FIGS. 5 to 7). As shown in FIG. 8, the female die 30 has a recess
33 in a portion corresponding to the projecting portion 32. The
inner shape of the recess 33 corresponds to the outer shape of the
return passage member 20.
Accordingly, when the female die 30 is pressed against the male die
31 with the material 29 being interposed therebetween as described
above, the material 29 is sandwiched between the projecting portion
32 and the recess 33 and is deformed. The return passage member 20
having the shape shown in FIGS. 5 to 7 is produced in this manner.
As shown in FIG. 10, the return passage member 20 thus produced has
the curved first and second connection portions 22, 23 connecting
to the linear portion 21. When the return passage member 20 is
produced as described above, the first and second connection
portions 22, 23 are formed by the curves of both longitudinal ends
of the projecting portion 32 of the male die 31 and the curves of
both longitudinal ends of the recess 33 of the female die 30.
As shown in FIG. 10, both longitudinal ends of the return passage
member 20 (material 29) are curved so as to form the first and
second connection portions 22, 23. This is implemented by
sandwiching and restricting both longitudinal ends of the return
passage member 20 (material 29) between the projecting portion 32
of the male die 31 and the recess 33 of the female die 30 as shown
in FIG. 11. Since the openings 22b, 23b are formed in the first and
second connection portions 22, 23 of the return passage member 20,
the process of curving both longitudinal ends of the return passage
member 20 (material 29) can be performed with the projecting
portion 32 being inserted from the portions of the material 29
which correspond to the openings 22b, 23b. This can restrain the
inside diameters of the first and second connection portions 22,
23, namely the inside diameters of the first and second connection
portions 22, 23 in the direction of the radius of curvatures of the
curves of the first and second connection portions 22, 23 (the
lateral direction in FIG. 11), from being reduced by deformation of
both longitudinal ends of the return passage member 20 when both
longitudinal ends of the return passage member 20 are curved.
Functions of the ball screw and the steering system will be
described below.
If the inside diameters of the first and second connection portions
22, 23 are reduced as described above, the balls 16 in the grooves
17 are subjected to increased resistance when they pass through the
first connection portion 22 and the second connection portion 23 to
recirculate through the first deflector 18, the return passage
member 20, and the second deflector 19 in the ball screw 15 having
the return passage member 20 attached thereto. Such increased
resistance hinders smooth flow of the balls 16. However, since
reduction in inside diameter of the first and second connection
portions 22, 23 is restrained, an increase in resistance the balls
16 are subjected to when passing through the first and second
connection portions 22, 23 can be restrained, whereby smooth flow
of the balls 16 can be achieved.
The present embodiment described in detail above has the following
advantageous effects.
When the balls 16 flowing in the grooves 17 are returned from
downstream to upstream through the return passage member 20 of the
ball recirculation system to recirculate in the ball screw 15, the
balls 16 can flow smoothly in the first and second connection
portions 22, 23 of the return passage member 20, and fluctuations
in rotation resistance of the ball nut 13 can be reduced.
The openings 21b, 22b, 23b in the outer periphery of the return
passage member 20 are formed along the entire longitudinal length
of the return passage member 20 so as to open toward the centerline
of the ball nut 13. Accordingly, when the return passage member 20
is produced, the first and second connection portions 22, 23 can be
formed by curving both longitudinal ends of the return passage
member 20 (material 29) with the projecting portion 32 being
inserted into the material 29 (return passage member 20) along the
entire length of the material 29 from the portions of the material
29 which correspond to the openings 21b, 22b, 23b. In this case,
when both longitudinal ends of the return passage member 20
(material 29) are curved in order to form the first and second
connection portions 22, 23, the projecting portion 32 has been
inserted in the return passage member 20 (material 29) along the
entire longitudinal length of the return passage member 20. This
can restrain the influence of the process of curving both
longitudinal ends of the return passage member 20 (material 29) on
the linear portion 21 of the return passage member 20.
The return passage member 20 is fitted in the attachment groove 26
formed in the outer peripheral surface of the ball nut 13, and the
openings 21b, 22b, 23b of the linear portion 21, the first
connection portion 22, and the second connection portion 23 of the
return passage member 20 are closed by the bottom surface of the
attachment groove 26. Since the return passage member 20 is fitted
in the attachment groove 26 formed in the outer peripheral surface
of the ball nut 13 and is connected to the first deflector 18 and
the second deflector 19, the return passage member 20 connecting
the first and second deflectors 18, 19 can be easily held in the
ball nut 13.
The driven pulley 71 is fitted on the outer peripheral surface of
the ball nut 13, and the return passage member 20 disposed in the
ball nut 13 is held against the ball nut 13 by the inner peripheral
surface of the driven pulley 71. This can restrain the return
passage member 20 from coming off from the ball nut 13 due to
clogging of the return passage member 20 with the balls 16 or due
to the centrifugal force generated by rotation of the ball nut
13.
For example, the above embodiment can be modified as follows.
The present invention is applicable to ball screws that are used in
devices other than steering systems. In such applications, the ball
screws may convert linear motion of the ball screw shaft to rotary
motion of the ball nut.
The return passage member 20 disposed in the ball nut 13 need not
necessarily be held by the inner peripheral surface of the driven
pulley 71.
In the case of not using the structure in which the return passage
member 20 is held by the inner peripheral surface of the driven
pulley 71, the attachment groove 26 in the outer peripheral surface
of the ball nut 13 may be omitted. In this case, the return passage
member 20 may be attached so as to project radially outward from
the outer peripheral surface of the ball nut 13, and the openings
21b, 22b, 23b of the return passage member 20 may be closed by the
outer peripheral surface (outer surface) of the ball nut 13.
In the return passage member 20, the opening 21b of the linear
portion 21 may be omitted, and only the first and second connection
portions 22, 23 may have the openings 22b, 23b. In this case, a
material having a tubular shape in a portion corresponding to the
linear portion 21 and having a plate shape in portions
corresponding to the first and second connection portions 22, 23
may be used to form the return passage member 20. In the case of
using such a material to form the return passage member 20, only
the portions of the material which correspond to the first and
second connection portions 22, 23 may be sandwiched between the
female die 30 and the male die 31 of the press die for producing
the return passage member 20, so that the first and second
connection portions 22, 23 are formed by the projecting portion 32
of the male die 31 and the recess 33 of the female die 30.
* * * * *